Compact device for continuous removal of water from an airstream-cascade screen

ABSTRACT

A separator for removing frozen or condensed water from an air stream, such as to aircraft environmental and avionics cooling systems, is described which comprises a generally tubular housing having an inlet and outlet, one or more screens of selected mesh size disposed in preselected spacing generally transverse of a direction of air flow within the housing, a brush or wiper disposed against each screen for removing moisture from each screen, either the screen or contacting brush being rotatable relative to the other, a motor operatively connected to the rotatable screen or brush for rotating one against the other to remove moisture from the screen, and a conduit operatively connected to the housing for draining moisture therefrom.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

BACKGROUND OF THE INVENTION

The present invention relates generally to environmental control systemsfor aircraft, and more particularly to a compact device for removingsuspended water, snow and ice from the air supply system of an aircraft.

Aircraft have environmental control systems (ECS) which may include anair supply for cabin air or avionics cooling which is connected to thecompressor region of the engine or auxiliary power unit (APU) of theaircraft. Bleed air at high temperature and pressure is conducted fromthe engine or APU, passed through a series of heat exchangers andvalves, and expanded through an air turbine to near ambient pressure toachieve the desired cooling. The cooled air at the turbine outletnormally is below about 32° F., is slightly above normal cabin pressure,and is saturated with water, a large portion of which condenses intoliquid and/or freezes. The fog or snow so produced is highly undesirablein the air fed to the cabin or avionics of the aircraft.

Conventional ECS systems of aircraft operate at an air flow rate ofabout 25 lb/min, turbine inlet pressure of about 45-60 psia and inlettemperature of about 150° F., and turbine outlet pressure of about 1.1psig. Fogging or icing occurs at the turbine outlet when the ambient airhas a moisture content of at least 90 grains of water per 1 b of air,which translates to ambient conditions where the air temperature is 60°F. at any humidity level or is higher than 60 ° F. at high relativehumidity. The foregoing analysis translates to a maximum needed iceremoval rate from the ECS turbine outlet of about 0.44 ft³ /hr.

In existing ECS systems, cold air at the turbine outlet is mixed withadditional warm bleed air to raise the air stream temperature abovefreezing, which severely reduces the overall cooling capacity of theECS. Mixing bleed air with the turbine outlet air can result in loss ofcooling capacity as high as 50%. Further. depending on the relativehumidity of the bleed air, mixing bleed air with cold turbine outlet aircan cause moisture to precipitate from the bleed air, which adds to thefogging problem. Using additional bleed air represents parasitic lossfrom the engine or APU and induces malfunctions and corrosion inavionics equipment. Therefore, a low pressure, low temperature waterseparator for removing condensed/frozen moisture at the outlet of theturbine is desirable.

The present invention solves or reduces in critical importance theproblems with the prior art and meets the desired criteria just statedby providing a low temperature, low pressure separator downstream of theexpansion turbine for removing water, snow or ice from the air supply ofthe ECS of an aircraft. The invention comprises in a representativeembodiment a plurality of spaced screens mounted within a tubularhousing, and upon which condensed or frozen water is captured byimpaction. The captured water is removed from the screens by a wiper orbrush. The screens may be rotatable within the chamber against astationary wiper or brush, or may be stationary and the wiper or brushmade to rotate against the screens. The water so removed is dischargedinto a container for recovery or into a drain for dispoal. A pluralityof cascaded screens may be included to attain a desired efficiency orcapacity of the separator. The invention may be constructed as a compactunit of less than about one cubic foot and may operate reliably atminimal pressure drop of two psi or less and collection efficiencygreater than 90%. The separator may be installed as an integral part ofan ECS on new aircraft or retrofitted to existing aircraft. Consideringthe undesirable alternative loss of cooling power suffered in existingECS systems where bleed air is used to warm the snow or fog, a smallpressure drop across the separator is acceptable while providingsignificant gain in ECS cooling capacity.

It is therefore a principal object of the invention to provide a devicefor removing condensed or frozen water from an air stream.

It is a further object of the invention to provide a compact device forremoving condensed or frozen water from an air supply to an aircraftcabin and avionics.

It is a further object of the invention to provide a device for removingcondensed or frozen water from an air stream using screens.

It is a further object of the invention to provide a compact reliabledevice for removing water particles from a high-speed gaseous streamwith low pressure differential across the device.

These and other objects of the invention will become apparent as thedetailed description of representative embodiments proceeds.

SUMMARY OF THE INVENTION

In accordance with the foregoing principles and objects of theinvention, a separator for removing frozen or condensed water from anair stream, such as to aircraft environmental and avionics coolingsystems, is described which comprises a generally tubular housing havingan inlet and outlet, one or more screens of selected mesh size disposedin preselected spacing generally transverse of a direction of air flowwithin the housing, a brush or wiper disposed against each screen forremoving moisture from each screen, either the screen or contactingbrush being rotatable relative to the other, a motor operativelyconnected to the rotatable screen or brush for rotating one against theother to remove moisture from the screen, and a conduit operativelyconnected to the housing for draining moisture therefrom.

DESCRIPTION OF THE DRAWINGS

The invention will be clearly understood from the following detaileddescription of representative embodiments thereof read in conjunctionwith the accompanying drawings wherein:

FIG. 1 is a schematic axial sectional view of a gas turbine enginehaving an ECS system and separator of the invention; and

FIG. 2 is a schematic axial sectional view of a representative screenseparator of the invention.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 1 shows a schematic axial sectionalview of a conventional gas turbine aircraft engine 10 connected to anECS system for the aircraft and incorporating the separator of theinvention. Engine 10 may conventionally comprise a suitable supportingstructure 11 defining air inlet and diffuser region 12, compressorregion 13, combustor region 14, afterburner 15 and discharge region orexhaust 16. Means may be provided near compressor region 13 of engine 10to provide a source of air under pressure for supplying theenvironmental control needs of the aircraft powered by engine 10.Therefore, means defining a conduit 17 may be included to supplycompressed air from compressor region 13 for conditioning by ECS system18 for subsequent use in cooling the cabin or avionics.

In accordance with the teachings of the invention, a separator 20 isdisposed downstream of ECS system 18 for removing excess moisture froman air stream supplying cabin and avionics cooling in the aircraft. Inoperation, air from ECS system 18 is expanded to suitable temperatureand pressure by expansion turbine 19 or the like included as part of ECSsystem 18.

Referring now also to FIG. 2, shown therein is a schematic axialsectional view of a representative embodiment of a screen separator 20of the invention which was built and tested in demonstration of theinvention. Separator 20 comprises a tubular housing 21 of suitableconventional material having an inlet 23 for operative connection to theoutlet of turbine 19 of ECS system 18 and outlet 25 for operativeconnection to the cabin or avionics systems requiring conditioned air.Inlet 23 may have conical shape as suggested in FIG. 2 (in thedemonstration unit a 31/2° conical diffuser) to provide some diffusionto air flowing from turbine 19. One or more screens (shown inrepresentative fashion in FIG. 2 as screens 27a, 27b, 27c) are disposedwithin housing 21 and suitably held using retaining rings 29a, 29b, 29cor the like. The screens are held in preselected spacing substantiallytransverse of the flow (left to right as viewed in FIG. 2) of airthrough separator 20. Any plurality of screens may be included in thestructure of separator 20, the three screens 27a, 27b, 27c shown in FIG.2 being exemplary of such plurality, and each screen defines a stage ofseparator 20. The number of stages (screens) selected for a particularapplication depends on the permissible pressure drop across the lengthof separator 20, which consideration includes screen sizes and spacings,housing dimensions, flow rates, operating temperature and pressure, andsnow accumulation and removal rates.

In the demonstration unit, housing 21 was sized at 6.75 inches innerdiameter (about 0.75 cubic foot) and the screens were spaced at 5.75inches to yield an acceptable pressure drop for typical flow rates andscreen sizes. The screens were of galvanized steel held by retainerrings of aluminum and were rotatably mounted on a shaft 31 operativelyconnected to a variable speed motor 33. Motor 33 controllably rotatesthe screens against respective brushes or wiper blades (wipers) 35disposed on one or both sides of the respective screens for removal fromthe screens of snow accumulation in the operation of separator 20.Brushes with metal or synthetic fibers or wipers or the like may beused. Wire brushes 35 were used in the demonstration unit of FIG. 2. Forclarity of illustration in FIG. 2, only one set of brushes 35 is shownas representative of respective sets disposed against each screen 27a,27b, 27c. Equivalent structure contemplated herein may comprise brushesor wipers 35 operatively connected to motor 33 for rotation againstrelatively stationary screens. Screen sizes which exhibited variousdegrees of snow accumulation in operation of the invention includedscreen wire diameters of from 0.9 to 10 mils and wire spacings from 1 to73 mils, with a typical screen size selected with 10 mil diameter wireand 46×73 mil spacing.

A collection tube 37 disposed near each screen and connected to outlet38 provides conduit means to collect and dispose of snow or wateraccumulation. Tubes 37 may be gravity drained or purged by controllablybleeding air from housing 21 through tubes 37.

Demonstration tests on a three-stage separator 20 were performed at atypical (uniform) ECS system 18 flow rate of 25 lb/min; screens 27a,27b, 27c were rotated at 20 rpm. Pressure drop across the unit typicallyincreased as the screens accumulated snow and substantially leveled outat about 2.5 psi after about 20 minutes.

The demonstration tests further showed that the precipitation at turbine19 outlet at temperatures below freezing has characteristics of finelyconstituted powdery snow rather than subcooled water droplets orgranular ice particles. The measured efficiency for the three stage unitof FIG. 2 corresponded to an efficiency of about 20% per stage (screen),which efficiency was higher than expected due to the characteristics ofthe snow versus that of spherical micron sized particle assumedtheoretically. The pressure drop across each screen was higher thanexpected because of high collection rates resulting from screen openarea significantly reduced by snow accumulation, which is in turnaffected by the snow removal rate provided by screen rotation ratesagainst brushes 35.

The invention therefore provides a low temperature, low pressureseparator for removing water, snow or ice from the air supply for theECS of an aircraft. It is understood that certain modifications to theinvention as described may be made, as might occur to one with skill inthe field of this invention, within the scope of the appended claims.All embodiments contemplated hereunder which achieve the objects of theinvention have therefore not been shown in complete detail. Otherembodiments may be developed without departing from the spirit of theinvention or from the scope of the appended claims.

We claim:
 1. A device for removing moisture from a gaseous streamcomprising:(a) a generally tubular housing having an inlet and outletfor flow therethrough of said gaseous stream; (b) a screen disposedwithin said housing generally perpendicular to said flow; (c) means forremoving moisture from said screen disposed within said housing incontact with said screen, said means for removing moisture and saidscreen disposed for relative movement therebetween; (d) a motor,operatively connected to one of said screen and said means for removingmoisture, for rotating said one of said screen and said means forremoving moisture relative to the other of said screen and said meansfor removing moisture; and (e) conduit means operatively connected tosaid housing for draining moisture therefrom.
 2. The device of claim 1wherein said means for removing moisture comprises a brush.
 3. Thedevice of claim 1 wherein said means for removing moisture comprises awiper blade.
 4. The device of claim 1 wherein said screen comprises 1 to10 mil wire in a mesh size of from 1 to 73 mils.
 5. In an environmentalcontrol system of an aircraft for conditioning air under pressure foruse within said aircraft, said environmental control system includingexpansion means for diffusing and cooling said air, an improvementcomprising a moisture separator operatively connected to the outlet ofsaid expansion means and including:(a) a generally tubular housinghaving an inlet operatively connected to said outlet of said expansionmeans and an outlet for flow therethrough of said air; (b) a screendisposed within said housing generally perpendicular to said flow; (c)means for removing moisture from said screen disposed within saidhousing in contact with said screen, said means for removing moistureand said screen disposed for relative movement therebetween; (d) amotor, operatively connected to one of said screen and said means forremoving moisture, for rotating said one of said screen and said meansfor removing moisture relative to the other of said screen and saidmeans for removing moisture; and (e) conduit means operatively connectedto said housing for draining moisture therefrom.
 6. The system of claim5 wherein said means for removing moisture comprises a brush.
 7. Thesystem of claim 5 wherein said means for removing moisture comprises awiper blade.
 8. The system of claim 5 wherein said screen comprises 1 to10 mil wire in a mesh size of from 1 to 73 mils.